B Is there any practical proof that quantum entanglement really works?

[sadaronjiggasha]

What i mean if we change state/spin at one end it will immediately effect the other. Can we see that live using two camera which may be 10 meter apart so that minium time delay. Is there any video proof exist such kind?

 

[PeroK]

What i mean if we change state/spin at one end it will immediately effect the other.

That's not what happens.

Can we see that live using two camera which may be 10 meter apart so that minium time delay. Is there any video proof exist such kind?

You can't watch elementary particles on video. Video works by a macroscopic object being bombarded with billions of photons. An electron may interact with a single photon, as it were, but you can't watch an electron spinning in real time like a pool ball.

In fact, even imagining a video of an electron spinning shows that you are not thinking about QM at all, but about a classical model of an elementary particle.

 

[Demystifier]

What i mean if we change state/spin at one end it will immediately effect the other.

Perhaps this would satisfy you: If you perform measurement at one end to create a random number, with appropriate entangled state this immediately guarantees that the random number at the other end will be the same. It's like instantaneous transfer of random "signal".

 

[sadaronjiggasha]

@Demystifier Its so mind boggling! Isn't it same as they both have similiar properties like twin and they are showing same random number at same time. I read somewhere if you think you understand QP actually you don't understand at all. Its always twist my head ups and down!

 

[PeroK]

I read somewhere if you think you understand QP actually you don't understand at all.

Don't believe everything you read.

 

[vanhees71]

Check out the material provided by the Nobel Foundation about this year's Physics Prize:

https://www.nobelprize.org/prizes/physics/2022/summary/

 

[Demystifier]

Isn't it same as they both have similiar properties like twin and they are showing same random number at same time.

The difference is that quantum measurement outcome did not exist before measurement, it was created by the measurement. There are contextuality theorems showing that it is not possible that the system had all values of measurement outcomes before the measurement.

 

[vanhees71]

Nevertheless it must be stressed that there is no spooky action at a distance, and you thus can't transmit a message faster than the speed of light!

 

[sadaronjiggasha]

@Demystifier Thanks for your answer. Can you suggest me any topics links or video link which will help me not thinking general way but quantum way. I read from schrödinger to current nobel winner zeilinger. Still I am thinking like general physics. How I can change that?

 

[PeroK]

@Demystifier Thanks for your answer. Can you suggest me any topics links or video link which will help me not thinking general way but quantum way. I read from schrödinger to current nobel winner zeilinger. Still I am thinking like general physics. How I can change that?

There's a fairly accessible introduction to QM at the undergraduate level here:

http://physics.mq.edu.au/~jcresser/Phys304/Handouts/QuantumPhysicsNotes.pdf

 

[Demystifier]

@Demystifier Thanks for your answer. Can you suggest me any topics links or video link which will help me not thinking general way but quantum way. I read from schrödinger to current nobel winner zeilinger. Still I am thinking like general physics. How I can change that?

Are you looking for something at the lay popular level? I know some good books at that level which are not free, for example Rae
https://www.amazon.com/dp/0521278023/?tag=pfamazon01-20

 

[sadaronjiggasha]

I am looking for something even may be one liner that will dramatically change my way of thinking. Putting all clasical physics behind me only thinking quantum way. Because I always try to understand anything by real life example. Then I can understand easily. But when I can't find any real life example I can't related to that. As QP physics does not relate to general physics I always mixed up QP to classic physics. How can I change that mind set?

 

[PeroK]

I am looking for something even may be one liner that will dramatically change my way of thinking.

The electron in the ground state of the hydrogen atom has zero angular momentum. It cannot be "going round" the nucleus if it has no angular momentum. In fact, it cannot be seen as orbiting the nucleus in the classical sense in any shape or form.

Instead, the hydrogen atom is defined by an energy state. How you imagine an energy state, other than by referring to pure mathenatics, is another question.

 

[sadaronjiggasha]

Like in double slit experiment when several eletron shooted and the pattern in the wall created, it hard to understand why that happen but when I saw video of water flowing into double slit and created the same pattern than it was so easy to understand. Visual representation of anything is very easy to understand.

 

[Nugatory]

What i mean if we change state/spin at one end it will immediately effect the other. Can we see that live using two camera which may be 10 meter apart so that minium time delay.

Not done the way you describe, but (I did this myself, in an undergraduate lab) we can set the photon source exactly midway between two polarizing filters. The particles in a pair are emitted moving in opposite directions, so they both reached their detectors at the same time - zero time lag between the measurements.

 

[Nugatory]

An unrelated subthread has been moved into its own thread: https://www.physicsforums.com/threads/quantum-mechanical-one-liners.1047137/

 

[StevieTNZ]

Like in double slit experiment when several eletron shooted and the pattern in the wall created, it hard to understand why that happen but when I saw video of water flowing into double slit and created the same pattern than it was so easy to understand. Visual representation of anything is very easy to understand.

https://press.princeton.edu/books/paperback/9780691176956/totally-random might be a good book for you.

 

[leonid.ge]

So if one entangled particle is here and the other in Alpha Centauri, and we measure our particle spin as +1, we know that the spin in Alpha Centauri is -1. In 5 minutes we measure the spin again and it is now -1. Does it mean it changed the spin because particle's spin can take values +/-1 with probability 0.5 or because the guys in Alpha Centauri measured their particle spin +1 ?

By the way, how can we know who measured the spin of their particle before and who after: us or them, if "before" and "after" in two remote systems is relative to observer?

 

[DaveC426913]

In 5 minutes we measure the spin again

No; the first measurement disrupts the entanglement. Subsequent measurements do not show entanglement.

By the way, how can we know who measured the spin of their particle before and who after: us or them, if "before" and "after" in two remote systems is relative to observer?

We can't. Unless we communicate (at c).

 

[PeroK]

By the way, how can we know who measured the spin of their particle before and who after: us or them, if "before" and "after" in two remote systems is relative to observer?

That's precisely the issue if you try to propose a FTL communication between the particles. Which way does the communication go if the order of measurements is frame dependent?

 

[leonid.ge]

But if entanglement is destroyed after the first measurement, then how would you use it for sending information? Even if you could, you would only do it once.

 

[PeroK]

But if entanglement is destroyed after the first measurement, then how would you use it for sending information?

You can't use it to communicate because you have no control over the measurements.

The question which perplexes people is how nature manages to achieve the measurement correlations.

 

[leonid.ge]

But if you destroy the entanglement by your measurement, then how there is correlation if the particles are no entangled anymore? You cannot guarantee that both sides do measurements on the two entangled particles simultaneously, because simultaneous does not exist when talking of remote systems. So one measures entangled particle whilst the other measures the not entangled one? A bit confusing.

 

[PeroK]

But if you destroy the entanglement by your measurement, then how there is correlation

The correlation applies to the initial measurement on each particle.

 

[DrChinese]

By the way, how can we know who measured the spin of their particle before and who after: us or them, if "before" and "after" in two remote systems is relative to observer?

No; the first measurement disrupts the entanglement. Subsequent measurements do not show entanglement.

Despite anyone's insistence otherwise: QM does NOT say anything about the ordering of measurements on entangled systems. It is not true that the first particle measured ends the overall entanglement any more than it is true that the second measurement ends the overall entanglement. This is simply unanswered in QM, and no experiment has ever demonstrated otherwise. Relativistic reference frame plays no part in such discussions.

1. You can in fact observe both particles (of a 2 particle entangled system) in the same exact reference frame. This way, there is no ambiguity about "first" and "second" in ordering. There is no observable conclusion that Alice influences Bob any more than Bob influences Alice.

2. A 2 particle system can be entangled on more than one basis. Ending entanglement on one does not automatically end entanglement on other bases. You could measure and demonstrate wavelength entanglement (for example) while spin/polarization entanglement is not affected.

3. All you can say is that a measurement on particle A by Alice leaves A unentangled on that basis for further measurements. Particle B can only be said to be unentangled (as of the time of the measurement on A) on that basis by assumption - nothing more. (Vice versa is "equally" true.) Keep in mind that an entangled system of 2 particles does not even require both particles have ever even coexisted! They don't even need to have interacted! Throw all your ideas about entanglement and causality out the window, there are none that can be demonstrated.

Please recall that all outcomes of entanglement measurements are random, as best can be determined. No way to extract FTL signals when that is the case.

 

[leonid.ge]

Suppose there is a new law: if measuring spin +1, then Biden will be president, otherwise Trump. Now, you went to Alpha Centauri and took with you one of the entangled particles leaving the other one on Earth. You measure you particle and see spin -1 which means the spin measured on Earth was +1, and you instantly know that Biden won. So you got information about who became president faster than speed of light.

 

[PeroK]

Suppose there is a new law: if measuring spin +1, then Biden will be president, otherwise Trump. Now, you went to Alpha Centauri and took with you one of the entangled particles leaving the other one on Earth. You measure you particle and see spin -1 which means the spin measured on Earth was +1, and you instantly know that Biden won. So you got information about who became president faster than speed of light.

That's not communication because the participants have no control of the message. They have a shared knowledge about the particles and implicit knowledge about any prearranged actions taken as a result of particle measurements.

Note that in particular there was no message anywhere in that scenario. It's only an assumption that things were carried out as arranged.

 

[StevieTNZ]

Suppose there is a new law: if measuring spin +1, then Biden will be president, otherwise Trump.

How do those get correlated?

 

[leonid.ge]

Is there an experiment confirming that correlations work on really large distances such as from here to other stars?

 

[DaveC426913]

It is not true that the first particle measured ends the overall entanglement any more than it is true that the second measurement ends the overall entanglement.

Sorry, that's not quite what I meant to imply. Apologies for any confusion.

I meant the first comparison of measurements between the two particles. They will show correlated entanglement. But if you try do the experiment a second time with the same two particles (which is what I assumed the OP was asking), there's no reason to expect a correlation.

 

[Vanadium 50]

Suppose there is a new law: if measuring spin +1, then Biden will be president, otherwise Trump... you instantly know that Biden won. So you got information about who became president faster than speed of light.

Supposed there is a new law passed that on election day a box is opened. If it contains a left shoe, Biden is elected and if it contains a right shoe, Trump is elected. The mating shoe is placed in another box and sent far away. When it is opened, the people who opened it instantly know the results of the selection faster than the speed of light.

This should make it clear that what you wrote has nothing whatever to do with quantum mechanics.

 

[berkeman]

Doh-dee-ohh-doh...

 

[Nugatory]

Is there an experiment confirming that correlations work on really large distances such as from here to other stars?

The best experiments so far have been done across thousands of kilometers.

It’s hard to see how we could do such an experiment at interstellar distances, both because of the practical difficulties in setting up two detectors light-years apart and because we would need at least one of the particles to traverse that enormous distance without blundering into something (stray grain of dust, random molecule floating around, cosmic ray particle, ….) which would break the entanglement.

However, nothing in our current physics says that quantum mechanics wouldn’t work as expected if we could overcome these practical difficulties in an experiment. We might imagine theories that aren’t quantum mechanics and agree with QM at planetary scale but predict different results at interstellar scale - but with neither a candidate theory nor experimental evidence suggesting that QM is wrong this is a completely sterile exercise.